Question: The expression $12g$ gives the number of kilometers a car can travel using $g$ liters of gasoline. How far can this car travel on $5 \dfrac12$ liters of gasoline?
Solution: A car with $5 \dfrac12$ liters of gasoline tells us that $g={5\dfrac12}$. Let's substitute $g={5\dfrac12}$ into the expression and evaluate: $\begin{aligned} &\phantom{=}12g\\\\ &= 12\left({5\dfrac12}\right)\\\\ &= {66} \end{aligned}$ A car can travel ${66} \text{ km}$ on ${5 \dfrac12}$ liters of gasoline.